Chapter 21 

 Subclass 2 Actinopoda Calkins 



THE Actinopoda are divided into two orders as follows: 

 Without central capsule Order 1 Heliozoa 



With central capsule Order 2 Radiolaria (p. 367) 



Order 1 Heliozoa Haeckel 



The Heliozoa are, as a rule, spherical in form with many radi- 

 ating axopodia. The cytoplasm is differentiated, distinctly in 

 Actinosphaerium, or indistinctly in other species, into the coarse- 

 ly vacuolated ectoplasm and the less transparent and vacuolated 

 endoplasm. The food of Heliozoa consists of living Protozoa or 

 Protophyta; thus their mode of obtaining nourishment is holo- 

 zoic. A large organism may sometimes be captured by a group of 

 Heliozoa which gather around the prey. When an active ciliate or 

 a small rotifer comes in contact with an axopodium, it seems to 

 become suddenly paralyzed and, therefore, it has been suggested 

 that the pseudopodia contain some poisonous substances. The 

 axial filaments of the axopodia disappear and the pseudopodia 

 become enlarged and surround the food completely. Then the 

 food matter is carried into the main part of the body and is di- 

 gested. The ectoplasm contains several contractile vacuoles and 

 numerous refractile granules which are scattered throughout. 

 The endoplasm is denser and usually devoid of granules. In the 

 axopodium, the cytoplasm undergoes streaming movements. The 

 hyaline and homogeneous axial filament runs straight through 

 both the ectoplasm and the endoplasm, and terminates in a point 

 just outside the nuclear membrane. When the pseudopodium is 

 withdrawn, its axial filament disappears completely, though the 

 latter sometimes disappears without the withdrawal of the pseu- 

 dopodium itself. In Acanthocystis the nucleus is eccentric (Fig. 

 165, 6), but there is a central granule, or centroplast, in the cen- 

 ter of the body from which radiate the axial filaments of the 

 axopodia. In multinucleate Actinosphaerium, the axilia filaments 

 terminate at the periphery of the endoplasm. In Camptonema, 

 an axial filament arises from each of the numerous nuclei (Fig. 

 163, d). 



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